Homeostasis involves balancing internal regulation and external adaptation. Regulation is more energetically costly than conforming to environmental conditions. Thermoregulation controls an animal's temperature through conduction, convection, radiation, and evaporation. Endotherms generate their own body heat through metabolic processes while ectotherms rely on external temperatures. While endothermy allows for activity in more environments, it requires more energy intake than ectothermy. Osmoregulation maintains the salt and water balance in organisms through mechanisms like gills, kidneys, and specialized epithelia that filter different nitrogenous wastes like ammonia, urea, and uric acid depending on the animal.

1. Homeostasis

2. Regulating vs Conforming
Difference between regulating and conforming
Why is regulation more energy expensive than
conforming?

3. Adaptation needs to outweigh the needs of the body
more than the benefits of the body

4. Balances
The natural environment is a system of balances
 Law of thermodynamics
Input and output should be equal
 When will there be an imbalance?

5. Thermoregulation
Temperature affects a lot of things
- Proteins
- Membranes
- What else?

6. Four physical processes of heat gain and loss
Conduction
Convection
Radiation
Evaporation

7. What is a wind chill effect?

8. Endothermy vs Ectothermy
Define endotherm/ ectotherm
True or false: ectotherms are always cold-blooded.

9. Advantages of endothermy
Longer vigorous activities than ectotherms
 Sustained activity is only possible in endotherms
 Thermal problems living in a terrestrial
environment is resolved through endothermy; e.g.
endotherms can live in below-freezing production-
temperature that deactivate the metabolism of
ectotherms

10. Disadvantage of endothermy
Thermoregulators invest more energy in their
activity than conformers, thus, increasing the energy
intake of regulators.

11. Question: why is ectothermy a good strategy in living
in a new environment?

12. Adaptation of animals that
thermoregulate
• Adjusting the rate of heat exchange between the
animal and its surroundings
• e.g. insulation such as feathers, fat
• changes in the circulatory system-
vasodilation/vasoconstriction
• countercurrent heat exchange- arteries are in
opposite direction that of veins in the extremities;
heat exchange is determined by physiology or
environment

13. Cooling through evaporative heat loss
Behavioural response- posture or movement
(migration/hibernation/estivation/winter sleep)
Changing the rate of metabolic heat- applies only to
endotherms

14. Mechanisms of temperature control
Mammals/ birds
 Constant heat loss
 Constant heat production
 Nonshivering thermogenesis vs shivering thermogenesis

15. Nonshivering thermogenesis (NST)
Hormones- inc metabolic activity of mitochondria
rather than production of ATP
Brown fat
Insulation
Blubber

16. Panting and evaporative cooling
Increase rate of heat exchange

17. How does fur/hair help in insulation?

18. Amphibians and Birds
Movement is key to heat production
Production of mucus to counter evaporative cooling
Reptiles have scales that inc skin’s SA
Vasoconstriction in extremities of marine iguana

19. FIshes
Mostly are conformers
Endothermic fishes use countercurrent heat
exchange system
Presence of special heat generating organs

20. Invertebrates
Aquatic invertebrates- mainly thermoconformers
Terrestrial invertebrates- same as vertebrate
ectotherms
Flying insects- smallest endotherms

21. Flying insects
Generate heat through flight muscles
Countercurrent exchange mechanisms
 Shutdown mechanisms during hot weather
Uses shivering in incubation
Huddling
Evaporative cooling
fanning

22. Thermostat
Controls temperature
Warm receptors- indicate inc in temp
Cold receptors- indicate dec in temp
What kind of mechanisms will each receptor
activate?

23. Below normal range?
Above normal range?

24. Acclimation vs acclimatization
Acclimation- laboratory
Acclimatization- natural environment

25. Antifreeze- used by ectotherms in sub-zero
environment
Proteins- e.g. Heat shock proteins

26. Torpor
Physiological state of low activity and low
metabolism
Hibernation vs winter sleep
Estivation
Daily torpor

27. Osmoregulation
Functions in maintaining the composition of the
cell’s cytoplasm
Mostly done indirectly
Open circulatory- uses hemolymph
Close circulatory- use interstitial fluid
Kidneys are specialized organs in maintaining the
composition of the body’s fluid composition

28. Transport epithelia
e.g. transport epithelium face the outside
environment to release unwanted solutes but have
tight junction in between cells to inhibit back flow;
functions like the Casparian strip of plants

29. Ammonia
Most common in aquatic animals
Can easily pass through membranes via diffusion
Invertebrates release ammonia all throughout the
body
Fish release ammonia in the form of ammonium ions
through the gills (kidneys excrete only minimal
amount)
Freshwater fishes excrete NH4 ions but also take in
Na ions through the gill epithelium to have a higher
concentration of Na ions compared to the
environment

30. Urea
less toxic compared to ammonia
Need less water in eliminating
Used by mammals, adult amphibians, marine fishes
and turtles
Ammonia+CO2
Transported via the circulatory system and filtered
in the kidneys

31. Can be transported in high concentration due to low
toxicity
Uses more energy
Animal adaptation: amphibians in water excrete
ammonia but excrete urea in land, what is the
advantage of this lifestyle?

32. Uric Acid
relatively nontoxic nitrogenous waste
Insoluble in water and excreted as semisolid paste
Advantage: low water loss
Disadvantage: highly expensive
Present in land snails, insects, birds, reptiles

33. Osmoconformers vs osmoregulators
Osmoconformers- animals that have the same
concentration of body fluid and of the external
environment; live in relatively stable environment
Osmoregulators- maintains the concentration of
body fluid; body fluid is not isoosmotic with that of
the environment

34. Stenohaline- animals that cannot tolerate broad
change in solute concentration
Euryhaline- animals that can tolerate substantial
change in external osmolarity, e.g. salmon